Described herein are elastomer surfaces and a process for providing elastomer surfaces, and more specifically to a fluoroelastomer or hydrofluoroelastomer surface on a fuser member useful in electrostatographic, including image-on-image, digital, and the like, apparatuses. In embodiments, a curative package comprising an amino silane and a biphenyl compound are used along with the fluoroelastomer. In embodiments, the amino silane has amino functionality. In embodiments, the biphenyl is a bisphenol. In embodiments, the amino silane has the following formula: NH2(CH2)nSi(CH3)3, wherein n is a number of from about 1 to about 25, or from about 1 to about 10, or from about 3 to about 6.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin and pigment particles which are commonly referred to as toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support, which may be the photosensitive member itself or other support sheet such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. To fuse electroscopic toner material onto a support surface permanently by heat, it is usually necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner causes the toner to be firmly bonded to the support.
Typically, the thermoplastic resin particles are fused to the substrate by heating to a temperature of between about 90° C. to about 200° C. or higher depending upon the softening range of the particular resin used in the toner. It is undesirable, however, to increase the temperature of the substrate substantially higher than about 250° C. because of the tendency of the substrate to discolor or convert into a fire, at such elevated temperatures, particularly when the substrate is paper.
Several approaches to thermal fusing of electroscopic toner images have been described. These methods include providing the application of heat and pressure substantially concurrently by various means, such as a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, and the like. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time are provided. The balancing of these parameters to bring about the fusing of the toner particles is well known in the art, and can be adjusted to suit particular machines or process conditions.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between the roll pair, or plate or belt members. The concurrent transfer of heat and the application of pressure in the nip affect the fusing of the toner image onto the support. It is important in the fusing process that no offset of the toner particles from the support to the fuser member take place during normal operations. Toner particles that offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the material being copied there. The referred to “hot offset” occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature is a measure of the release property of the fuser roll, and accordingly it is desired to provide a fusing surface, which has a low surface energy to provide the necessary release. To ensure and maintain good release properties of the fuser roll, it has become customary to apply release agents to the fuser roll during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils to prevent toner offset.
Fusing systems using fluoroelastomers as surfaces for fuser members are described in U.S. Pat. No. 4,264,181 to Lentz et al., U.S. Pat. No. 4,257,699 to Lentz, and U.S. Pat. No. 4,272,179 to Seanor, all commonly assigned to the assignee of the present invention. The disclosures of each of these patents are hereby incorporated by reference herein in their entirety.
U.S. Pat. No. 5,017,432 describes a fusing surface layer obtained from a specific fluoroelastomer, poly(vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene) where the vinylidenefluoride is present in an amount of less than 40 weight percent. This patent further discloses curing the fluoroelastomer with VITON® Curative No. 50 (VC-50) available from E.I. Du Pont de Nemours, Inc., which is soluble in a solvent solution of the polymer at low base levels and is readily available at the reactive sites for crosslinking. This patent also discloses use of a metal oxide (such as cupric oxide) in addition to VC-50 for curing.
U.S. Pat. No. 5,061,965 to Ferguson et al. discloses an elastomer release agent donor layer comprising poly(vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene) where the vinylidenefluoride is present in an amount less than 40 weight percent and a metal oxide. The release agent donor layer is cured with a nucleophilic curing agent in the presence of an inorganic base.
Generally, the process for providing the elastomer surface on the fusing system member includes forming a solvent solution/dispersion by mixing a fluoroelastomer dissolved in a solvent such as methyl ethyl ketone and methyl isobutyl ketone, a dehydrofluorinating agent such as a base, for example the basic metal oxides, MgO and/or Ca(OH)2, and a nucleophilic curing agent such as VC-50 which incorporates an accelerator and a crosslinking agent, and coating the solvent solution/dispersion onto the substrate. The surface is then stepwise heat cured. Prior to the stepwise heat curing, ball milling is usually performed, for from 2 to 24 hours.
Curing can be considered important in the preparation of fluoroelastomers surfaces. The level of cure is important in that it affects the high temperature stability along with both chemical and physical properties of the elastomers. High temperature stability is of significance for fusing subsystem applications, whereas incomplete curing can adversely effect the transfer efficiencies of liquid and dry toners. Fluoroelastomers have been cured as set forth above, comprising the addition of dehydrofluorinating agents. The dehydrofluorinating agents create double bonds, which provide crosslinking cites on the fluoroelastomer. Examples of curing agents include peroxides (for example, bis (2,4-dichlorobenzoyl) peroxide, di-benzoyl peroxide, di-cumyl peroxide, di-tertiary butyl peroxide, and 2,5-dimethyl-2,5-bis (t-butyl peroxy) hexane), diamines, hydrides, oxides, and the like. The preferred curing agents are the basic metal oxides (MgO and Ca(OH)2) and aliphatic and aromatic amines, where the aromatic groups may be benzene, toluene, naphthalene, anthracene, and the like. The particularly preferred curing agents are the nucleophilic curing agents such as VC-50 which incorporates an accelerator (such as a quaternary phosphonium salt or salts) and a crosslinking agent (bisphenol AF). VC-50 is preferred due to the more thermally stable product it provides. The curative component can also be added after ball milling in a solution form. The resulting elastomer is provided on a substrate. Normally, step heat curing occurs next by heat curing at about 93° C. for 2 hours, followed by 2 hours at 149° C., 2 hours at 177° C. and 16 hours at 208° C.
Known curing processes require the addition of curing agents and crosslinking agents, in addition to dehydrofluorinating agents such as the basic metal oxides, MgO and Ca(OH)2. These curing and crosslinking agents, along with the basic metal oxides, increase the cost of the curing process immensely. In addition, roll milling and/or ball milling are normally required in known curing procedures wherein basic metal oxides are used. Roll milling and/or ball milling can be an extremely costly and time-consuming procedure, requiring anywhere from 2 to 24 hours to complete. In addition, the curing procedure is to be followed very carefully and in specific detail in order to form fluoroelastomers with sufficient chemical, physical and thermal stability, along with sufficient toughness.
Moreover, developer and/or toner resins, especially low melt toner resins, tend to react with the metal oxides present in the cured fluoroelastomer surface causing them to bind to the metal oxides. The result is that toner adheres to the surface of the fuser member, resulting in hot offset. An additional failure mode observed in coatings cured with metal oxides, is the phenomenon of particulate “pick-out” that is the result of oxide particles near the surface being ripped out of the elastomer during operation. This can leave voids in the coating surface, which are then easily filled by toner and toner additive materials.
Some of the above problems have been met by improved methods for providing an outer fluoroelastomer surface, such as those methods described in the following patents.
U.S. Pat. No. 5,700,568 discloses a fusing system member having a supporting surface and a basic metal oxide-free outer surface layer of the reaction product of a fluoroelastomer, a polymerization initiator, a polyorganosiloxane and an amino silane.
U.S. Pat. No. 5,695,878 discloses fluoroelastomer surfaces for fusing members and methods for fusing including a method for forming the outer surface including dissolving a fluoroelastomer, adding an amino silane to form a resulting homogeneous fluoroelastomer solution; and subsequently providing a layer of the homogeneous fluoroelastomer solution to the supporting substrate.
U.S. Pat. No. 5,744,200 discloses a method for providing a volume grafted fluoroelastomer outer fuser surface by dissolving a fluoroelastomer in a solvent, adding a nucleophilic dehydrofluorinating agent, such as an amino silane, a polymerization initiator and a polyorganosiloxane, optionally adding an additional amount of amino silane as a curative, and subsequently providing the layer of the homogeneous volume grafted fluoroelastomer on a supporting substrate.
U.S. Pat. No. 5,750,204 discloses a method for providing a fluoroelastomer surface by dissolving a solid fluoroelastomer in a solvent, adding an amino silane, and subsequently providing a layer of the fluoroelastomer on the supporting substrate.
U.S. Pat. No. 5,753,307 discloses a method for providing a fluoroelastomer surface by dissolving a fluoroelastomer, adding a dehydrofluorinating agent, adding an amino silane, and providing the layer on the substrate.
The above patents disclose use of an amino silane as both the coupling and crosslinking, or as both a dehydrofluorinating agent and a curing agent. The amino silanes disclosed in these patents has the following formula: NH2(CH2)nNH2(CH2)mSi[(OR)t(R′)w] wherein n and m are numbers from about 1 to about 20, and preferably from about 2 to about 6; t+w=3; R and R′ are the same or different and are an aliphatic group of from about 1 to about 20 carbon atoms, such as methyl, ethyl, propyl, butyl, and the like, or an aromatic group of from about 6 to about 18 carbons, for example, benzene, tolyl, xylyl, and the like. Examples of amino silanes given in the patents include 4-aminobutyldimethyl methoxysilane, 4-aminobutyl triethoxysilane, (aminoethylaminomethyl)phenyl triethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyl dimethoxysilane, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, N-(2-aminoethyl)-3-aminopropyl tris(2-ethyl-hexoxy)silane, N-(6-aminohexyl)aminopropyl-trimethoxysilane, 3-(1-aminopropoxy)-3,3-dimethyl-1-propenyl-trimethoxysilane, 3-aminopropyl tris(methoxyethoxyethoxy)-silane, 3-aminopropyldimethyl ethoxysilane, 3-aminopropylmethyl diethoxysilane, 3-aminopropyl diisopropylethoxysilane, 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, or 3-aminopropyltris (trimethylsiloxy)silane. Particularly preferred amino silanes listed in the patents are AO700 (N-(2-aminoethyl)-3-aminopropyl trimethoxysilane), 3-(N-strylmethyl-2-aminoethylamino) propyltrimethoxy silane hydrochloride and (aminoethylamino methyl), phenethytrimethoxy all manufactured by Huls of America, Inc.
However, the methods set forth in the above patents did not produce smooth surfaces, which are necessary particularly when the surfaces come in contact with image surfaces. In fuser members, for example, intimate physical contact between the final image and the fuser surface is achieved, and the surface defects on the fuser can transfer to the image, resulting in defects and life shortfalls. Common cure systems involve insoluble metal oxides and inorganic bases, which contribute to a fair amount of surface texture in a cured fluoroelastomer film. The inorganic bases are necessary for dehydrofluorination of the backbone, allowing for a bisphenol AF to crosslink at the site of unsaturation. The roughening effect of the insoluble particle addition has been avoided in the past by extended ball milling or grinding of particulate additives or through the use of soluble aminosilanes. Amino silanes can act as both the base and as the crosslinking agent, resulting in a completely soluble fluoroelastomer coating formulation. Amino silanes may, however, be susceptible to changes in humidity, resulting in inter-oligimerization and potential variability in physical properties and extent of cure.
Therefore, a method for producing a smoother outer fluoroelastomer fuser member surface, along with a method that uses an amino silane that is less susceptible to changes in humidity and has less of a potential to inter-oligomerize or have variability in physical properties and extent of cure, is desired.
The fuser system member described herein, and method of preparation, uses an amino silane as the dehydrofluorinating species in a fluoroelastomer cure system, and is combined with bisphenol AF or other similar biphenyl species as the crosslinking molecule. This results in an effective crosslinking system, while maintaining the desired state of a fully soluble crosslinkable coating system. While diamines are effective as crosslinkers in fluoroelastomers (e.g., DIAK 1, DIAK 3, AO700), in embodiments, the desired amino functional molecule described herein includes an amino silane that has only amine functionality. In embodiments, the amino silane does not have methoxy or ethoxy groups present, as they tend to undergo hydrolysis reactions during cure. These hydrolysis reactions can lead to several problems due to condensation, reaction with humidity, and other problems. Since bisphenol crosslinkers have improved high temperature properties over diamines, it is desirable to use these crosslinkers in a way that does not require insoluble additives such as inorganic bases and metal oxides. In embodiments, the amino silane has only amino functionality. In embodiments, the amino silane has the following general formula: NH2(CH2)nSi(CH3)3, wl , or from about 3 to about 6.